Di(sulfonylamide) salts such as bis(fluorosulfonyl)amide alkali metal salts (M+[(FSO2)2N]−) are useful as ionic conducting materials or electrolytes or additives available in secondary cells (Patent Document 1, Patent Document 2). In the case where the compounds are used as electrolytes, it has been reported that the smaller amount of impurities, such as water, ash, SO42−, or residual solvents, in the compounds, is more preferable (Non-Patent Document 1, Patent Document 3).
Various methods are known as a method for producing a bis(fluorosulfonyl)amide salt. For example, according to Non-Patent Document 2, a bis(fluorosulfonyl)amide potassium salt is obtained by reacting a compound with potassium fluoride, the compound being obtained by reacting sulfamic acid, thionyl chloride, and chlorosulfonic acid. According to Non-Patent Document 2, a bis(fluorosulfonyl)amide potassium salt is obtained by conducting filtration to separate crystals precipitated by adding dropwise methylene chloride into a concentrated solution obtained by separating a reaction liquid obtained by the above-mentioned reaction.